1. Field of the Invention
The present invention relates to the field of rotating machines.
2. Brief Description of the Related Art
In the case of machines subjected to high thermal and mechanical load, such as, for example, compressors, gas turbines, or steam turbines, it is desirable to reduce mechanical stresses by means of a suitable design of the individual machine and plant parts.
Thus, for example, it is known from the prior art (see EP-A1-0 945 594 or U.S. Pat. No. B1-6,478,539), in the moving blades of gas turbines, to design the transition from the blade leaf to the adjoining blade platform lying below it with a predetermined, preferable elliptic curvature contour, the large major axis running in the radial direction and the small major axis being oriented parallel to the surface of the platform.
Furthermore, it is known from U.S. Pat. No. B1-6,237,558 to provide specific locations of the crankcase of an internal combustion engine which are critical in terms of mechanical stresses with a curvature which follows a conic section (ellipse, hyperbola, parabola).
Not only the moving blades of turbines are exposed to high mechanical loads due to the high rotational speed, but also the rotor shaft itself. Critical locations are in this case, above all, the slots in the rotor shaft which are arranged on the outer circumference and, running in the axial direction or running around annularly, may be provided, for example, for receiving the blade roots of the moving blades or as part of a shaft seal. Where such slots are concerned, the stresses occurring in the slots depend critically on the cross-sectional contour. GB-A-2 265 671 or U.S. Pat. No. 4,818,182 disclose, for the fastening of moving blades, slots which run around annularly and which have a rounded cross-sectional contour. No information is given as to the nature of the curved profile or the influence of the contour on the stresses in the slot.